The recent UNAIDS 90-90-90 guidelines set ambitious targets for scale-up of HIV treatment: ?By 2020, 90% of all people living with HIV will know their HIV status?, 90% of all people with diagnosed HIV infection will receive sustained antiretroviral therapy (ART)?, 90% of all people receiving antiretroviral therapy will have viral suppression?.[1] Reaching these goals will require expansion of existing programs and implementation of new strategies. This proposed cost-effectiveness analysis will examine a novel test and treat strategy for achieving the first and second `90s' through early HIV diagnosis and rapid linkage to HIV care, including ART. This approach improves HIV detection through frequent testing using tests that detect both acute and established HIV infection as well as rapid linkage to HIV care through the use of peer health navigators. Our hypothesis is that early intervention (ART and risk reduction services), especially during acute HIV infection (AHI) when viral load is high, will be cost-effective due to lower health care costs and reduced HIV transmission among high-risk populations such as men who have sex with men (MSM). We test this hypothesis among MSM in Lima, Peru, where there is a concentrated epidemic with high rates of HIV. Our research in Lima indicates that identifying MSM with AHI is feasible and that there is a demand among MSM for such a testing program. Intervention effectiveness and cost data are available from the recently completed 4-year SABES study which followed over 2000 MSM with monthly testing for HIV RNA and antibodies to detect incident HIV infections shortly after acquisition. The SABES study used peer navigators to assure rapid linkage of HIV+ participants to care and same-day ART initiation. Our hypothesis is that increased detection of acute/early HIV infection and rapid linkage to HIV care and ART incurs fewer costs overall and improves health more than the current practice of semi-annual serologic HIV testing and patient referral to treatment centers. Moreover, the differences will be driven by HIV care costs avoided as well as longer and better quality lives. Aim 1. Model the transmission of HIV within the MSM population in Lima, Peru and estimate the number of new HIV infections averted through increased detection and rapid linkage to care of MSM with recently acquired HIV. Developing a detailed mathematical model of HIV transmission among MSM, parameterized with the data from SABES, will allow us to explore the population-level effectiveness of the intervention in scenarios of future expansion of ART and possible introduction of pre-exposure prophylaxis. Aim 2. Estimate the cost-effectiveness of increased detection and rapid linkage to care of MSM with recently acquired HIV, detected during acute HIV infection, from the health system and patient perspectives. Aim 2A. Estimate the 10-year individual and health system costs with increased detection and rapid linkage to care of MSM with acute HIV. Aim 2B. Adjust predicted life years saved in Aim 1 for quality of life and estimate the cost per disability adjusted life-year averted compared to the national standard of care.